The use of wood stoves or open fire-places and the like heating apparatuses is on the increase, because of the considerable increase in recent times of heating fuel prices. Previous patents have presented inventions with means for extraction of a major portion of the heat from the fire and projecting it into the room, to increase the thermal efficiency of the system; for example, Billmeyer's U.S. Pat. No. 4,095,581, issued June 20, 1978; Meyes' Canadian Pat. No. 1,090,225, issued Nov. 25, 1980; Hannum's Canadian Pat. No. 328,702, issued Feb. 14, 1928; and Bennett's Canadian Pat. No. 296,067, issued Nov. 30, 1926. In another patent, Collard's Canadian Pat. No. 760,240, issued June 6, 1967, an air generator is added to convey the air at a given speed within a tire grate. Further, in Rae's U.S. Pat. No. 4,151,827, issued May 1, 1979, an electric-driven blower circulates the air from the room through a heat exchanger forming the rear wall component of the fire-place.
All these inventions embody improvements in the thermal efficiency of the stove or fire-place. However, the circulated air is heated only when a fire is active within the stove or fire-place. It may be appropriate to find a way to lengthen the heating period of the circulating air before having to feed more fuel into the fire.